The gastrointestinal tract (GIT) of humans and animals contains a complex microbial ecosystem that is relatively stable over time, but can be affected by dietary changes, antibiotics, or infection. The resulting instability puts the host at isk for opportunistic infection. This study examines the role of microbes in the GIT and how they contribute to host health by resisting infection and reducing this instability. In particular, this research examines how gut microbes may mitigate opportunities for infection by consuming specific carbohydrate residues from dietary glycans. The proposed experiments examine the generation of free sialic acid by the gut microbiota from a sialylated bovine milk glycopeptide. Sialic acid is known to be key substrates that contribute to opportunistic infections. The proposed studies will examine the fate of this glycopeptide in vivo, measure differences in the concentration of sialic acid residues by in feces during supplementation with this glycopeptide and a probiotic that consumes the glycopeptide, in comparison to un-supplemented controls. In concert, the microbial communities will be examined by next-generation sequencing of bacterial 16S rRNA amplicons, to track changes in the microbiota, specifically the Enterobacteriaceae resulting from supplementation. These experiments will also determine whether supplementation with these species of Bifidobacterium and glycopeptide are able to reduce pathogen colonization in an animal model challenged with enterotoxigenic Escherichia coli. Together, these studies seek to unravel the food-web interactions of gut microbes in an animal model and how these interactions may contribute to host health. The experiments also evaluate the safety of sialylated milk glycopeptide. The requested support will train the applicant in highl relevant techniques including mass spectrometry, experience with microbial community sequencing and analysis, and extensive experience working in a relevant large animal model.